Cody's Lab. A lot of channels do cool shit for their youtube channel, and it feels like Cody has a youtube channel for the cool shit he's already doing. Like, vacuuming out a chicken coop. Check out how he does it without dirtying the filter on his shop vac. Or an infinite pickle jar. With a couple design modifications, that could legit be a marketable product.

Also Know Art. I can't even imagine the effort it takes to make the 3d models he uses to explain things, but damn if I don't know a hell of a lot more about telescoping mechanisms and drills and buttons and phones and staplers and saws and like a million other things because of their amazing channel